As the call for reducing battery usage is becoming popular, the need for miniaturized high-performance electric generators has emerged. One such device is the hub-type dynamo for bicycles, which is considered to be an artistic electric generator design producing reasonable small resistance. According to specifications relating to bicycle illumination, the dynamo, received in the limited space of a bicycle hub, is required to drive a 12 ohm light bulb to illuminate slightly when the bicycle is cruising at a low speed, i.e. about 5 km/h, and to suppress the raising of voltage outputted when cruising at a higher speed. Thus, when designing a hub-type dynamo, multi-pole structure is most popular.
The common hub-type dynamo is originated from the coaxial multi-pole hub design of Sturmey-Archer bicycle hub. One such design can be seen in both U.S. Pat. No. 5,769,750, entitled “Epicyclic change gear system”, and U.S. Pat. No. 5,813,937, entitled “Epicyclic change speed gear system”, respectively claimed priority to GB Pat. No. 9409844 and 9304189. Such coaxial multi-pole hub is characterized in that: a plurality of poles are provided and arranged in an alternating manner while enabling the plural poles to be wrapped by a tube-like magnet, and is vastly implemented by various electric generators. One such application is seen in TW Pat. No. 94109740, entitled “Hub-type dynamo and bicycle”, also claimed priority to JP Pat. No. 2004-190663, in which a hub-type dynamo 10 is disclosed, as seen in FIG. 1 and FIG. 2. The hub-type dynamo 10 is comprised of: a permanent magnet 14, arranged inside a shell 12 of the dynamo 10; and a spindle 11; wherein the spindle further comprise: a plurality of poles 74, 75, arranged in a manner enabling the polar of each pole to be faced toward that of the permanent magnet 14; two stator pins 16, 17, arranged on the circumference thereof; and a coil 22, arranged between the two stator pins 16, 17. By the use of two positioning components 30, 31, arranged on the spindle 11, to hold and fix the stator pins 16, 17 in respective, the two stator pins 16, 17 are fixed to the spindle 11. Moreover, the fixing of the two stator pins 16, 17 on the spindle 11 is characterized in that: there is a recess hole 15 formed in each stator pin 16, 17 while enabling each recess hole 15 to channel with a hole 13 bored through the spindle 11; and there is an insulator arranged between each stator pin 16, 17 and its corresponding positioning component 30, 31 for preventing the crossing of electricity from an electricity-conducting member, placed next to each positioning component 30, 31, to the stator pins 16, 17. The aforesaid coaxial multi-pole electric generator is further characterized in that: by the forming of such recess hole 15, the generation of eddy current can be prevented and thus the efficiency of the electric generator is improved. However, although the generators with coaxial multi-pole design are popular and vastly adopted, it has shortcomings listed as following:
(1) The magnet is shaped like a tube and is warping around the stator pins that cause the resulting electric generator to be bulky and costly.
(2) The plural poles will guide and cause the corresponding magnetic lines to defect more than twice that cause the magnetic flux passing through the coil to drop.
(3) As each stator pin shall have a specific 3-D shape and each magnetic line is deflected more than twice, and moreover, the magnetic fields between the plural poles are easily to interfere with each other, the overall electric generation efficiency is low.
Please refer to FIG. 3, which is a hub-type dynamo disclosed in TW Pat. No. 92137088. The hub-type dynamo of FIG. 3 is comprised of a hub 2, a coil seat 3, a coil structure 4, an iron core 5, a casting set 6, two magnetic blocks 7 and a bearing axle 8. Moreover, a conventional hub-type dynamo 1 is also disclosed in TW Pat. No. 92137088, as shown in FIG. 4, which is comprised of a hub 11, a coil seat 12, a coil structure 13, an iron core 14, a casting set 15, a magnetic ring 16 and a bearing axle 17. As disclosed in the Taiwan patent, the conventional hub-type dynamo 1 has two shortcomings. One of which is that the size of the conventional hub-type dynamo 1 can not be reduced effectively since the iron core 14, the coil structure 12, the coil seat 13, the casting set 15 and the magnetic ring 16 are being received in the hub 11 from inside out and in a layer-by-layer manner. Another is that, since the iron core 14 is substantially a silicon steel lamination that is formed by stacking a plurality of silicon steel sheets 141 in a one-by-one manner, the formation and installation of the iron core 14 is complicated that it is time-consuming and uneconomical. With reference to the shortcomings of the conventional hub-type dynamo 1, the hub-type dynamo 2 adopted the two magnetic blocks 7, instead of using a conventional tube-like magnet, while enabling the two to be placed along the axial direction X respectively at the two sides of the casting set 6, so that the diameter of the hub 2 and volume thereof can be reduced. It is noted that the reduced diameter should be twice the thickness of the magnet. In addition, comparing the hub-type dynamo of FIG. 3 with that of FIG. 4, not only the magnetic ring 16 is replaced and substituted by the two magnetic blocks 7, but also the appearances of the two casting sets 6, 17 are totally different. Although each component of the casting set 6 of FIG. 3 is constructed with a plurality of radially extended claws, each of the plural claws is not bended. That is, as the two components of the casting set 6 is placed respectively at the two sides of the coil structure 4 along the axial direction, the claws of one component will not interlace with those of another component, which has nothing in common with the conventional casting set 15. For those skilled in the art, the design of the aforesaid casting set 6 is serious defected and is not realistic. It is noted that as the way the claws being arranged, only half the surface area of each magnetic block 7 can be utilized, moreover, there will be circuits happening between the unused magnetic block 7 and the casting set 6, and thus the efficiency of electricity generation is severely reduced. As for the formation and installation of the conventional iron core 14, it is solved in the Taiwan patent by previously using a pin 52 to hold and position the plural steel sheets 51 into an iron core 5 so that the installation of the iron core 5 can be facilitated. However, for those skilled in the art, the aforesaid solution is also not realistic. As seen in FIG. 4, the direction of the stacking of the plural silicon steel sheets 141 to form the conventional iron core 14 is perpendicular to the magnetic lines, i.e. the X direction, by which the iron core 14 can have good permeance and such stacking is common in devices such as transformers and motors, etc. However, the direction of the stacking of the plural silicon steel sheets 51 to form the iron core 5 is parallel to the X direction, by which the hysteresis loss and eddy current loss are increased. Therefore, it is not a good idea to cause a serious efficiency drop just for reducing volume and simplifying assembly, as the hub-type dynamo disclosed in TW Pat. No. 92137088.
Please refer to FIG. 5, which shows a flat rotary electric generator disclosed in U.S. Pub. No. 20040135452. In FIG. 5, as a toroidal coil structure 1 is sandwiched between two matching disc-shaped magnetic pole structures 2 and as the dimension of the winding of the toroidal coil structure 1 is restricted and limited, when multi-pole design is adopted while enabling each pole to be a section of one disc-shaped magnetic pole structures 2 bounded by two radii, the volume enclosed within the two matching sections respectively of the two matching disc-shaped magnetic pole structures 2 is also restricted and must be considered. Therefore, the overall diameter of the flat rotary electric generator can not be reduced effectively. In addition, the overall size is required to be increase when it is intended to have high efficiency. Thus, the aforesaid flat rotary electric generator can not be miniaturized while increasing power density.
From the above description, it is noted that as the hub-type dynamo can be easily integrated with the roller brake that is suitable to be applied in the mass production of bicycle, the improvement of the efficiency of the hub-type dynamo while reducing the cost thereof can be a great boost for bicycle industry, as well as other applications requiring portable power generator. Moreover, as hub-type dynamo is common in the magnetic resistance system of currently available fitness bicycle, it is preferred to have a highly efficient hub-type dynamo in the fitness bicycle since not only the power generating efficiency is improved, but also the cost can be reduced. In addition, a miniature power generator, being the improvement over the hub-type dynamo, is in great need, since it can be received in pocket, shoe sole, glasses, watch, etc., to be used as backup or emergency power for those portable electronic devices, such as RF radio, or cellular phone, and so on. Therefore, it is required to have a cheap, small-sized electric generator capable of generating sufficient power.